This invention relates to water-in-oil emulsion type explosive compositions containing highly divided, high density, non-explosive materials which not only act as a fuel and/or densifying agent but also act as a detonation sensitizer. In particular, the invention relates to the incorporation of highly divided, high density, non-explosive materials such as ferrophosphorus, ferromanganese, ferrosilicon, sand or alumina which is added to the oil phase of a water-in-oil emulsion explosive. The term "sensitizing/densifying agent" as used herein will mean highly divided, high density, non-explosive materials which not only increase the density of water-in-oil emulsion explosives compositions but which also sensitize such compositions. In another aspect, the invention relates to the emulsion explosives having increased low temperature detonation sensitivity in small diameters at unexpectedly high densities.
The invention relates to water-in-oil emulsion explosive compositions containing an aqueous solution of inorganic oxidizer salt that is emulsified as a dispersed phase within a continuous carbonaceous fuel phase, and the sensitizing/densifying agent of the present invention. The water-in-oil emulsion explosives compositions of the present invention can also include bulking agents, additional fuels, and auxiliary sensitizers. Water-in-oil emulsion type blasting agents (i.e. explosive compositions not detonable by a No. 6 or less powerful blasting cap) were first disclosed by Bluhm in U.S. Pat. No. 3,447,978. After the disclosure of water-in-oil emulsion blasting agents, various approaches were taken to produce a emulsion explosive which was cap sensitive, i.e. detonable by a No. 6 or less powerful blasting cap. U.S. Pat. No. 3,779,522 suggests the addition of materials such as trinitrotoluene, pentaerythritol tetranitrate, and the like to conventional water-in-oil blasting agents will render them cap sensitive. However, it is well known that such materials are explosives and are more expensive than conventional ingredients that are utilized in the manufacture of water-in-oil emulsion blasting agents. Also, these compositions do not adequately perform in small diameters boreholes and are undesirable from other standpoints.
The preparation of water-in-oil emulsion explosive compositions which were rendered cap sensitive without the use of an explosive ingredients were disclosed in U.S. Pat. Nos. 3,715,247 and 3,765,964. These patents disclose the addition of a detonation sensitizer or catalyst, such as an inorganic metal compound of Atomic Number 13 or greater, and strontium compounds. While the compositions disclosed in these patents exhibited improved low temperature detonability they do not disclose a detonability of temperatures as low as -5.degree. C.
Other attempts to produce a water-in-oil emulsion explosive with good low temperature detonability in small diameters using a fatty acid amine or ammonium salt emulsifier having a chain link ranging from 14 to 22 carbon atoms were disclosed in U.S. Pat. No. 4,141,767. However, this patent do not disclose a high density, emulsion explosive detonable in small diameters at high density.
Thus, there has been a continuing need for a small diameter, high density emulsion explosive composition which is inexpensive, detonable at low temperatures in small diameters with good detonation pressure. In one aspect, the present invention provides for a cap or cord sensitive emulsion explosive composition with improved low temperature detonability at high densities and small diameters. This is accomplished by the inclusion of a sensitizing/densifying agent of finely divided, high density, non-explosive materials, such as ferrophosphorus, ferrosilicon, ferromanganese, alumina or sand.
It is well known in the art that increasing the density of a water-in-oil emulsion explosive composition decreases its sensitivity. It is also well known in the art that the sensitivity of emulsion explosives also depends on the intimacy of the oxidizer/fuel blend. In general, the more intimate the mixture of the oxidizer and fuel phases of an emulsion the more sensitive the emulsion. Thus, those skilled in the art would expect that adding densifying agents in particulate form would desensitize rather than sensitize water-in-oil emulsions explosive compositions. Thus, it is really quite amazing that known densifying agents when sufficiently finely divided would function to increase the sensitivity of an emulsion explosive rather than to desensitize it.